<template>
  <div class="pagination">
    <button :disabled="pageNo ==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button @click="$emit('getPageNo',1)" v-if="startNumAndEndNum.start>1" :class="{active:pageNo ==1}">1</button>
    <button v-if="startNumAndEndNum.start>2">···</button>

    <!-- 中间部分 -->
    <span v-for="(page, index) in startNumAndEndNum.end" :key="index">
      <button :class="{active:pageNo ==page}" @click="$emit('getPageNo',page)"
        v-if="page>=startNumAndEndNum.start">{{page}}</button>
    </span>

    <button v-if="startNumAndEndNum.end < totalPage-1">···</button>
    <button :class="{active:pageNo == totalPage}" @click="$emit('getPageNo',totalPage)"
      v-if="startNumAndEndNum.end < totalPage">{{totalPage}}</button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props: ["pageNo", "pageSize", "total", "continues"],
    computed: {
      //总共有多少页
      totalPage() {
        return Math.ceil(this.total / this.pageSize)
      },
      //计算出连续的页码的起始数字个结束数字
      startNumAndEndNum() {
        //解构一下this的值
        let {
          pageNo,
          continues,
          totalPage
        } = this
        let start = 0
        let end = 0
        if (continues > totalPage) {
          //不正常情况
          start = 1;
          end = totalPage;
        } else {
          //正常情况
          start = pageNo - parseInt(continues / 2)
          end = pageNo + parseInt(continues / 2)
          //start为小于1  纠错
          if (start < 1) {
            start = 1
            end = continues
          }
          //end为最大页码数
          if (end > totalPage) {
            end = totalPage
            start = totalPage - continues + 1
          }
        }
        return {
          start,
          end
        }
      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;

    .active {
      background-color: skyblue;
    }

    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
</style>